A semiconductor chip equipped with an integrated circuit (particularly, CPU) and a power transistor generating a large amount of heat is generally has an air-cooled or water-cooled heat sink mounted thereon. A semiconductor relay substrate (e.g., silicon interposer) equipped with a semiconductor chip generating a large amount of heat has a similar heat sink mounted thereon.
To increase adhesion and thermal conductivity between such a semiconductor substrate generating a large amount of heat and a heat sink for efficient heat dissipation, a member called heat spreader (typically, a metal plate or a metal film) is joined on a heat dissipation surface of the semiconductor substrate to achieve a configuration such that the heat sink is connected directly or via a joining layer to the heat spreader. Copper, copper alloy, and aluminum are frequently used as a material of the heat spreader. A metal paste, a thermally-conductive adhesive, a solder, a thermally-conductive grease, etc. are used for joining the semiconductor substrate and the heat spreader.